1. Field of the Invention
The present invention relates to a clockwise and counterclockwise rotation switching device provided on a motor-driven power tool for switching a rotation direction of a motor.
2. Description of the Background Art
A clockwise and counterclockwise rotation switching device for a power tool includes a unit base being fixed to a stator of a motor in a housing and having a pair of fixed contacts electrically connected with a coil of the stator, respectively, and a ring-shaped brush base holding a pair of carbon brushes, which face a commutator with the surface thereof in sliding contact with the commutator, and being rotatably attached to the unit base. A pair of movable contacts is provided between the fixed contacts in the brush base, respectively. Clockwise or counterclockwise rotation of the motor can be selected by switching a contact mode of both the movable contacts with respect to the fixed contacts, the switching being caused by a rotating operation of the brush base (for example, refer to Japanese Unexamined Patent Publication No. 2003-180054).
FIG. 6 is a resolved perspective view to illustrate a particular example of a clockwise and counterclockwise rotation switching device. FIG. 7 is an assembled perspective view of the device. In a clockwise and counterclockwise switching device 1, a disk-ring shaped unit base 2 is fixed to a stator of a motor, and a short sleeve shaped brush base 3 is coaxially attached at an upper part of the unit base 2 and has the approximately same diameter as that of the unit base 2. Both the unit base 2 and the brush base 3 are made of a synthetic resin.
The unit base 2 includes a pair of circular-shaped fixed contacts 4 and 4 in a plane view in a point symmetric manner. An end part of the each fixed contact 4 mutually faces the other fixed contact with a predetermined interval therebetween in a peripheral direction, and serves also as elastic end 4a being movable in a radius direction. An insertion piece 5 is continuously connected with each fixed contact 4 and inserted into one pair of terminals on a coil side of the stator so as to be electrically connected. Lower ends of terminal metals 6 and 6 are inserted into the other pair of terminals on the coil side and upper ends thereof are connected with a switch. Connection parts 7, 7, connected to the terminal end of the stator with holding the insertion piece 5 and the terminal fitting 6 are formed at a lower side of the unit base 2. Further, a pair of hooks 8 and 8 is upwardly projected at an inner periphery of the unit base 2. An upper end of each of the hooks 8 and 8 is outwardly folded. The hook 8 is engaged with recessed parts 9 and 9 formed in the peripheral direction on an inner periphery of the brush base 3, so that the brush base 3 is rotatably connected on the unit base 2.
Then, the brush base 3 is equipped with square sleeve shaped metallic brush holders 10 and 10 on a straight line at positions of point symmetry. The brush holder 10 can hold a carbon brush (not illustrated) mounted thereon. Further, as illustrated in FIG. 8A and FIG. 8B each brush holder 10 is connected with movable contacts 11 and 11 lower ends of which project and abut with lower ends of the brush base 3 at the point symmetry positions of the brush base 3. Each movable contact 11 is projected between the fixed contacts 4 and 4 of the unit base 2.
Therefore, when the movable contacts 11 and 11 are moved in the peripheral direction caused by the rotation of the brush base 3, the movable contacts 11 and 11 are moved to the inner peripheral side of two pairs of the elastic ends 4a and 4a which becomes point symmetry at the fixed contacts 4 and 4, and contacted with the elastic end 4a while outwardly bending the elastic end 4a on the outer periphery side. Then, the clockwise and counterclockwise rotation of the motor is switched. In addition, FIG. 8A and FIG. 8B illustrate a neutral state in which the movable contacts 11 and 11 are not contacted with any fixed contact 4. Further, the brush base 3 has operation projections 12 and 12 on the side thereof, and each operation projections 12 is outwardly projected through a window formed on the side of the housing of the power tool. The operation projections 12 and 12 enable the brush base 3 to be rotationally operated from outside of the housing.